Annual report pursuant to Section 13 and 15(d)

Basis of Presentation - Effects of Prior Period Errors in Consolidated Statements of Comprehensive Income (Detail)

v2.4.0.8
Basis of Presentation - Effects of Prior Period Errors in Consolidated Statements of Comprehensive Income (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
As Previously Reported [Member]
Sep. 30, 2012
As Previously Reported [Member]
Jun. 30, 2012
As Previously Reported [Member]
Mar. 31, 2012
As Previously Reported [Member]
Dec. 30, 2011
As Previously Reported [Member]
Sep. 30, 2011
As Previously Reported [Member]
Jun. 30, 2011
As Previously Reported [Member]
Mar. 31, 2011
As Previously Reported [Member]
Dec. 31, 2012
As Previously Reported [Member]
Dec. 31, 2011
As Previously Reported [Member]
Dec. 31, 2010
As Previously Reported [Member]
Dec. 31, 2012
As Adjusted [Member]
Sep. 30, 2012
As Adjusted [Member]
Jun. 30, 2012
As Adjusted [Member]
Mar. 31, 2012
As Adjusted [Member]
Dec. 31, 2011
As Adjusted [Member]
Sep. 30, 2011
As Adjusted [Member]
Jun. 30, 2011
As Adjusted [Member]
Mar. 31, 2011
As Adjusted [Member]
Dec. 31, 2012
As Adjusted [Member]
Dec. 31, 2011
As Adjusted [Member]
Dec. 31, 2010
As Adjusted [Member]
Condensed Financial Statements, Captions [Line Items]                                                                  
Net income $ 112,200 $ 111,900 $ 132,000 $ 107,900 $ 110,100 $ 107,500 $ 108,600 $ 88,800 $ 463,962 $ 414,959 $ 292,883 $ 117,881 $ 117,779 $ 133,368 $ 108,162 $ 105,357 $ 108,022 $ 111,180 $ 88,019 $ 477,190 $ 412,578 $ 299,215 $ 112,207 $ 111,873 $ 131,951 $ 107,931 $ 110,072 $ 107,459 $ 108,601 $ 88,827 $ 463,962 $ 414,959 $ 292,883
Total comprehensive income                 $ 470,076 $ 404,435 $ 288,994                 $ 483,304 $ 402,054 $ 295,326                 $ 470,076 $ 404,435 $ 288,994